Typical coaxial cable includes one or more layers of conductive materials for radio frequency (RF) shielding. One common type of shielding material is a conductive tape that attenuates interfering electromagnetic fields more efficiently in the high frequency range. Another common type of shielding material is a conductive braid that attenuates interfering electromagnetic fields more efficiently in the low frequency range. The combination of tape and braid layers as shielding material in a coaxial cable is sometimes referred to as an outer conductor. For example, a standard-shield coaxial cable includes a center conductor surrounded by a dielectric, an outer conductor including a conductive tape and a conductive braid, and a jacket. The cable is also generally terminated with cable connectors.
One problem associated with coaxial cables is that moisture present in and around the cable can corrode the cable conductors. This corrosion negatively affects the electrical and mechanical properties of the cable. The moisture can enter the cable in several ways. For example, moisture can enter the cable through small breaks in the jacket or through improper or defective connectors. Further, moisture can enter the cable during the jacket extrusion process or during storage in high humidity environments.
Past efforts to reduce moisture-related corrosion in coaxial cables have generally focused on methods of saturating the space between the jacket and the cable conductors with a flooding compound, such as ETPR, polybutane, polybutene, amorphous polypropylene, and polyisobutylene. While these flooding methods are generally effective at reducing moisture-related corrosion, the flooding compounds themselves are relatively sticky and/or waxy. These sticky and/or waxy flooding compounds often remain on the fingers and tools of cable installation technicians after cutting or terminating a flooded coaxial cable.
Another past effort to reduce moisture-related corrosion in coaxial cables is disclosed in U.S. Pat. No. 6,997,999 (the '999 patent). The '999 patent discloses a corrosion-inhibiting composition that is applied to the outer conductor of a coaxial cable. The corrosion-inhibiting composition disclosed in the '999 patent includes three main elements: 1) a paraffinic oil, 2) a corrosion-inhibiting compound dispersed in the paraffinic oil, and 3) a stabilizer to maintain the dispersion between the corrosion-inhibiting compound and the oil. The corrosion-inhibiting compound disclosed in the '999 patent is preferably a petroleum sulfonate salt such as a calcium salt having an activity of greater than 0% to about 25% based on the calcium salt.
The '999 patent teaches that the stabilizer is necessary to prevent the preferred amounts of the corrosion-inhibiting compound from precipitating out of the oil. Specifically, the stabilizer allows for larger amounts of the corrosion-inhibiting compound (about 15% by weight or greater) to be used in the corrosion-inhibiting composition without precipitation of the corrosion-inhibiting compound. The '999 patent teaches that the corrosion-inhibiting composition preferably includes the corrosion-inhibiting compound in an amount of from about 15% to about 30% by weight. Therefore, the '999 patent teaches that the preferable amount of the corrosion-inhibiting compound would not be possible without the presence of the stabilizer. Unfortunately, however, the inclusion of a stabilizer, which is necessitated by the ues of a petroleum sulfonate salt, increases the cost and complexity of a corrosion-inhibiting composition.